<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8"/>
    <title></title>
    <meta name="viewport"
          content="width=device-width,user-scalable=0,initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0">
    <script>
        var scale = 1 / window.devicePixelRatio;
        document.querySelector('meta[name="viewport"]').setAttribute('content', 'width=device-width,initial-scale=' + scale + ', maximum-scale=' + scale + ', minimum-scale=' + scale + ', user-scalable=no');
        document.documentElement.style.fontSize = document.documentElement.clientWidth / 10 + 'px';
    </script>
    <style>
        body {
            margin: 0;
            padding: 0;
        }

        .wrapper {
            margin: auto;
            max-width: 750px;
        }

        .box {
            width: 2.66666667rem;
            height: 2.66666667rem;
            background: red;
        }
    </style>
</head>
<body>
<div class="wrapper">
    <div class="box"></div>
</div>
</body>
</html>
